Pressure sensors can be used to measure the pressure of a fluid. For example, some conventional pressure sensors have been fabricated using commercially available bulk quartz resonators. Quartz is a piezoelectric crystal having highly stable elastic properties with low intrinsic losses. Because of these properties, quartz has been widely utilized in precision frequency control applications, such as timing and clocking for electronic instruments.
Despite having a very precise oscillation frequency, the resonance frequency of quartz is also very sensitively affected by a variety of environmental disturbances such as external forces, bending, compression, mass loading and acceleration. The fractional deviation of the resonance frequency from its original value f0 is given by Δf/f0. One frequency shifting mechanism in quartz resonator sensors occurs when a force is applied along the radial direction at the periphery of a circularly shaped thickness-shear-mode (TSM) quartz resonator. The quartz sensor produces a frequency shift proportional to the amplitude of the applied force. This phenomenon is defined as the force-frequency effect.
Notably, quartz is sensitive not only to in-plane radial forces, but also to transverse forces and flexural bending. Thus, transverse forces may be induced by several means in order to exploit quartz as a pressure sensor. However, current pressure sensors using quartz resonators are only suitable for very high pressure measurements, typically at pressure levels of about one atmosphere and above. Current quartz pressure sensors are also unable to effectively measure pressure over a wide pressure range.